Dark diversity of Odonata in Amazonian streams.

The biological diversity of a region may not be fully sampled due to the low abundance or rarity of species, or the absence of species determined by their niche specificity. Investigating these species is essential for understanding the unrealized ecological potential in different habitats, identifying gaps in local and regional communities, and gaining a better understanding of the impacts of environmental changes. Therefore, to expand knowledge about the diversity of Odonata in Eastern Amazonia considering the absent species, we tested the hypotheses that: 1) Environmental variables will influence dark diversity, with greater explanation by canopy cover where sites with lower canopy cover will have higher dark diversity values, and; 2) Functional traits associated with better species dispersal will be correlated with low dark diversity of Odonata, such as larger and wider wings for example. For this, adult Odonata specimens were sampled, while structural habitat characteristics and physical and chemical water variables were measured in 128 first- to third-order streams in the Eastern Amazon. Morphological and behavioral data were recorded for each specimen. Generalized linear models were applied to predict the effects of habitat structural characteristics and physical and chemical water variables on the dark diversity of Odonata. Additionally, we assessed which functional traits contribute most to the variation of dark diversity within these communities. Habitat structural features and physical and chemical water variables had no effect on dark diversity. Morphological traits, such as body conformation, with species having narrower wings, longer hind wings, narrower thoraxes, and shorter abdomens, comprised most of the dark diversity. The dispersal limitations of some Odonata species strongly suggest the role of space and time in nature planning and management.